System and method for improved optical measurements during rheometric measurements

Abstract

A rheometric system includes an optical encoder coupled to a rotating shaft and configured to detect a rotational position of the shaft with respect to a reference. The rotational information is forwarded to a program or memory. An optical rotation plate is mechanically fastenable to the rotating shaft. A laser is provided to probe optical properties of a fluid sample proximate to the optical rotation plate. The system includes a detector system for measuring laser light scattered or transmitted through the sample chamber. The detector system is coupled to a memory that stores optical data collected after light impinges on the optical plate. Experimental fluid sample optical data and background optical data are each stored as a data structure that creates a point by point map of rotational position of the sample plate with the optical data collected thereat. A program or routine is provided that can correct point by point along the optical rotation plate the experimental sample optical data using the background optical data.

1. A system for enhancing optical measurements in a rheometer, comprising:
 a light source to provide light incident on a fluid sample; 
 a rotatable optical plate that is substantially transparent to the light source and configured to impart a stress or strain within a fluid disposed within the rheometer; 
 a position transducer configured to measure a plate angular position of the rotatable optical plate; 
 a detector system for measuring transmitted light signals from light passing through the rotatable optical plate; and 
 a memory coupled to the detector system and configured to receive and store background optical data and experimental sample optical data based on the transmitted light signals, the memory further including a data structure that is arranged to provide a set of point by point background corrected optical data, wherein each data point of the background corrected optical data corresponds to a unique location of the rotatable optical plate. 
 
   
   
     2. The system of  claim 1 , wherein the rotating optical shaft is mechanically detachable from the rotatable optical plate. 
   
   
     3. The system of  claim 1 , further comprising a processor that is configured to manipulate the background data and experimental sample data to produce the background corrected optical data. 
   
   
     4. The system of  claim 1 , wherein the detector system comprises:
 an analyzer configured to polarize portions of the modulated beam transmitted by the fluid sample and to pass an analyzed beam; 
 a detector that detects the analyzed beam; and 
 a scattered light detector for detecting light originating in the modulated beam and scattered from the fluid sample. 
 
   
   
     5. The system of  claim 1 , background optical data corresponds to optical measurements performed on light intersecting the rotatable optical plate without the presence of the fluid sample, and wherein the experimental sample optical data corresponds to measurements performed on light intersecting the rotatable optical plate in the presence of the fluid sample. 
   
   
     6. The system of  claim 1 , wherein the experimental sample optical data corresponds to measurements performed in the presence of an experimental fluid, and wherein the background optical data comprises data from measurements taken in the presence of an index-matched fluid whose index of refraction substantially matches that of the experimental fluid. 
   
   
     7. The system of  claim 1 , wherein the position transducer is coupled to a rotating shaft that is configured to rotate in unison with the rotatable optical plate. 
   
   
     8. The system of  claim 7 , wherein the point by point background corrected optical data comprises data taken from optical measurements performed at a plurality of locations on the rotatable optical plate, the plurality of locations corresponding to a plurality of angular positions located around an entire circumference of a circle concentric with a rotation axis of the rotating shaft. 
   
   
     9. The system of  claim 8 , wherein the plurality of angular positions are regularly spaced. 
   
   
     10. The system of  claim 8 , wherein each angular position corresponds to a measurable portion of the rotatable optical plate that is configured to intersect the light source, wherein the plurality of angular positions are mutually spaced such that no overlap occurs among measurable portions. 
   
   
     11. An optical rheometer having optical measurement capabilities, comprising:
 a lead optics module that provides a source of polarized laser light incident on a fluid sample; 
 a rotary optical encoder coupled to a rotating shaft and configured to measure an angular position of the shaft; 
 a rotatable optical plate mechanically fastenable to the rotating shaft; 
 a detector system for measuring transmitted light signals from light passing through the rotatable optical plate; 
 a memory coupled to the detector system that is configured to receive and store background optical data and experimental sample optical data based on the transmitted light signals; and 
 a plurality of data structures each configured to provide a set of point by point mapping of optical data to respective optical plate positions, wherein at least one data structure comprises background corrected optical data obtained by mapping point by point background data to respective fluid sample data. 
 
   
   
     12. The system of  claim 11 , wherein the lead optics module comprises:
 a laser that provides the source of polarized light and is configured to provide a beam incident at a substantially normal angle upon the optical plate, wherein at least a portion of the beam is transmitted through the rotatable optical plate; 
 a polarizer configured to polarize the incident beam and pass a polarized beam; 
 a photoelastic modulator configured to receive the polarized beam and to pass a modulated beam containing a first component of the polarized beam that is retarded with respect to a second component; 
 a quarter wave plate; and 
 a fixed optical plate having a portion that substantially transmits the modulated beam. 
 
   
   
     13. A system for enhancing optical measurements in a rheometer, comprising:
 a sample chamber configured to house, alternately, an experimental fluid sample and an index-matched background fluid having a substantially similar refractive index as that of the experimental fluid sample; 
 a light source configured to direct light toward fluid contained in the sample chamber; 
 a rotatable optical plate that is substantially transparent to the light source and configured to impart a stress or strain within a fluid disposed within the sample chamber; 
 a position transducer configured to measure a plate angular position of the rotatable optical plate; 
 a detector system for measuring transmitted light signals from light received from the light source and passing through the rotatable optical plate, 
 wherein the system is configured to store data from optical measurements performed on the index-matched fluid and experimental fluid sample in respective background and experimental fluid sample data structures, each of the data structures comprising a plurality of optical measurements made at a corresponding plurality of plate angular positions. 
 
   
   
     14. The system of  claim 13 , wherein the detector system comprises:
 an analyzer configured to polarize portions of the modulated beam transmitted by the fluid sample and to pass an analyzed beam; 
 a detector configured to detect the analyzed beam; and 
 a scattered light detector for detecting light originating in the modulated beam and scattered from the fluid sample. 
 
   
   
     15. The system of  claim 13 , wherein the position transducer is coupled to a rotating shaft that is configured to rotate in unison with the rotatable optical plate. 
   
   
     16. The system of  claim 15 , wherein the rotating optical shaft is mechanically detachable from the rotatable optical plate. 
   
   
     17. The system of  claim 13 , further comprising:
 a processor operable on a program that is configured to manipulate the background data and experimental fluid sample data structures to produce a background corrected optical data structure; and 
 a memory coupled to the detector system and configured to receive and store in respective data structures the background optical data and the experimental fluid sample optical data, and configured to the background corrected optical data structure. 
 
   
   
     18. The system of  claim 17 , wherein the background data structure, experimental fluid sample data structure, and background corrected optical data structure each comprise a set of optical values that are point by point data mapped to corresponding locations on the rotatable optical plate from which the corresponding set of optical values are derived. 
   
   
     19. The system of  claim 18  wherein each of the background data structure and the experimental fluid sample data structure comprise a common set of plate angular positions, wherein the background corrected optical data structure comprises a plurality of data points resulting from point by point subtraction of the background optical data from the experimental fluid sample data. 
   
   
     20. The system of  claim 18 , wherein the corresponding locations comprise a plurality of angular positions located around at least a portion of a circumference of a circle concentric with a rotation axis of the rotating shaft. 
   
   
     21. The system of  claim 20 , wherein the plurality of angular positions are regularly spaced. 
   
   
     22. The system of  claim 20 , wherein each angular position corresponds to a measurable portion of the rotatable optical plate that is configured to intersect the light source, wherein the plurality of angular positions are mutually spaced such that no overlap occurs among measurable portions.